The present disclosure relates generally to ultrasound imaging. In particular, the present disclosure relates to Capacitive Micromachined Ultrasonic Transducers (CMUTs) that are integrated with complementary metal oxide semiconductor (CMOS) circuits, and methods for forming the same.
CMUTs are known devices that include a membrane above a micromachined cavity. The membrane may be used to transduce an acoustic signal into an electric signal, or vice versa. Thus, CMUTs can operate as ultrasonic transducers.
Many different types of images can be formed using ultrasound devices. The images can be real-time images. For example, images can be generated that show two-dimensional cross-sections of tissue, blood flow, motion of tissue over time, the location of blood, the presence of specific molecules, the stiffness of tissue, or the anatomy of a three-dimensional region.
Two types of processes can be used to fabricate CMUTs. One approach involves a sacrificial layer process to form the membrane of the CMUT on a first substrate above a sacrificial layer. Removal of the sacrificial layer results in the membrane being suspended above a cavity. In another approach, a wafer bonding process bonds two wafers together to form a cavity with a membrane.